It is known to produce sodium percarbonate by reaction of a soda solution or suspension with aqueous hydrogen peroxide according to the formula EQU Na.sub.2 CO.sub.3 + 1.5 H.sub.2 O.sub.2 .fwdarw.Na.sub.2 CO.sub.3 . 1.5 H.sub.2 O.sub.2 (I)
and thereby reduce the solubility of the percarbonate formed by the addition of inert salts, such as sodium chloride (Swiss Pat. No. 90295).
In British Pat. No. 568,754 there is described the continuous production of sodium percarbonate from hydrogen peroxide and sodium carbonate in which the necessary amounts of hydrogen peroxide and sodium carbonate are only added in small portions to the reaction solution. Simultaneously, the particle structure of the percarbonate is improved by the use of active oxygen stabilizers such as magnesium compounds and is also favorably influenced by the addition of sodium hexametaphosphate.
The disadvantage of the process is, as stated, that the addition of soda and hydrogen peroxide is only carried out in small portions and reaction times are provided between the additions. During the feeding of the materials the temperature increases from 15.degree. to 22.degree. C. and is held at this temperature until the end of the reaction. This process leads to a fine, granular, free flowing percarbonate.
Furthermore, according to German DS. No. 2 328 803 there is obtained an abrasion resistant coarse percarbonate by reaction of a soda solution or suspension which contains 2-8 grams of sodium hexametaphosphate per liter of solution with a hydrogen peroxide solution containing 3-10 grams of magnesium ions per liter of solution, in a given case in the presence of sodium chloride.
Great importance is placed on the exact observance of the amounts of sodium hexametaphosphate and magnesium ions added. Otherwise there are formed fine or non-resistant particles.
The disadvantage of the process which is only carried out discontinuously is that in the reuse of the mother liquor the yield of hydrogen peroxide is greatly reduced at the high soda dissolving temperature of 24.degree. C. because of active oxygen decomposition. This decomposition is further increased in using industrial soda because of the concentrating of impurities in the mother liquor.
Because of this decomposition of active oxygen which continues during the feeding of the hydrogen peroxide the sodium percarbonate crystallization conditions cannot be held constant.
The ratio soda/sodium percarbonate is displaced to favor the soda, which as the most readily soluble component exerts an additional pressure on the sodium percarbonate still present in the solution. The net result is a too quick crystallization, a fine particle product is obtained.
In contrast, the object of the invention is the continuous production of a compact, coarse sodium percarbonate with small active oxygen loss while holding the crystallization conditions as constant as possible with reuse of the mother liquor.